Image measuring apparatuses for making three-dimensional measurements of an object to be measured on the basis of image information acquired by an image capturing device may include, for example, one which employs the interference of white light having a wide spectrum width (the so-called WLI (White Light Interferometer) measurement) or one which employs contrast information (the so-called PFF (Points From Focus) measurement). Such an image measuring apparatus measures the three-dimensional shape of an object to be measured from the image information that is acquired at each vertical position by operating an image capturing device to scan in the vertical direction relative to a stage. Such an image measuring apparatus has been increasingly required, for example, of measurement in wider ranges in which the size of an object to be measured does not fall within one field of view of the image capturing device.
As a preparatory step for performing measurement in wider ranges, there has been a method for identifying a measurement range in advance with the help of CAD data (the offline teaching) (Japanese Patent Application Laid-Open No. 2008-201914). This method is to simplify the setting of measurement ranges with reference to design values.
On the other hand, there has also been a method including performing a preparatory measurement in advance in a short time using a low-power lens of a resolution coarser than desired for actual measurement, and identifying a desired measurement range on the basis of the acquired image (Japanese Patent No. 6095486).